1. Field of the Invention
The present invention relates to methods and apparatus for handling of packaged integrated circuits.
2. The Prior Art
Production of integrated circuit (IC) chips involves considerable handling, particularly of packaged IC's during the burn-in and test phases. Efficient production requires fully automatic transfer of IC's, for example, from carrying-tray bins to burn-in-board sockets and, after burn-in, back to carrying-tray bins. Transfer must be fast, avoid damage to the IC's and the sockets, assure correct placement of the IC's in the sockets so that device functionality can be checked, and permit sorting of the IC's based on results of the burn-in operation.
An example of a system for loading and unloading IC's on burn-in boards is the BLU300 Burn-In Board Loader/Unloader, commercially available from Schlumberger ATE Automated Systems, Westerville, Ohio, USA. Such a system can be adapted for use with bum-in boards of various sizes, can be fitted with component tooling to handle IC's having various package types, and can be programmed for automated operation in various modes.
Burn-in boards (BIB's) used in such a system typically have an array of sockets, each of which receives a single packaged IC. FIGS. 1A, 1B and 1C show one type of commercially-available "Zero Insertion Force" (ZIF) socket 100 used on BIB's, in respective top, side elevation and end views. FIGS. 2A, 2B and 2C show a type of IC package 200 intended to be inserted in such a socket, in respective top, side elevation and end views. ZIF socket 100 has a body 105 opposed rows of spring contacts 110 and 115, a cover 120, and rows of connector pins 125 and 130. Cover 120 is resiliently biased upwardly as shown. When cover 120 is pressed downwardly, spring contacts 110 and 115 are retracted so that an IC package 200 can be dropped into the well area of socket 100 without resistance. When IC package 200 is in place and cover 120 is allowed to return to its upward position, spring contacts 110 and 115 extend toward the center of socket 100 to make electrical contact with respective rows 205 and 210 of pins of IC package 200.
While generally effective, the use of such ZIF sockets has drawbacks. The cost of the sockets is higher than for "Low Insertion Force" (LIF) sockets of the type described below with reference to FIGS. 3A-3C. The BIB area required for ZIF sockets is greater than that for LIF sockets, primarily because of the area required for the cover surrounding the well area of the ZIF socket, such as cover 120. Thus, fewer IC's can be loaded on each BIB with ZIF sockets than might be possible with LIF sockets. The tooling required to load IC's into ZIF sockets is complicated by the need for an actuator to depress the cover before an IC can be inserted or removed and to release the cover after an IC is dropped into or picked out of the socket. The need to move the cover down and then up again adds to the time needed each time an IC is inserted in or removed from the ZIF socket. When the IC is dropped into the ZIF socket, gravity and chamfered walls in the upper portion of the chip well are all that can guide the IC into correct position. If the IC is not sufficiently aligned with the well before being dropped in, it may not seat properly and may have to be removed for another try. Because there is little or no sliding contact between the ZIF socket's spring contacts and the IC's pins, surface corrosion and impurities which may interfere with electrical conductivity are not displaced during the insertion process.
FIGS. 3A, 3B and 3C are sectional views showing one type of commercially-available "Low Insertion Force" (LIF) socket 300. FIGS. 3A and 3B are a sectional views taken along centerline 3A/3B--3A/3B of FIG. 3C. FIG. 3C is a sectional view taken along centerline 3C--3C in FIGS. 3A and 3B. Socket 300 has a socket body 305 with a well 310 for receiving an IC, horizontally-opposed rows of contact springs 315 and 320, and horizontally-opposed rows of connector pins 325 and 330. Precise alignment of an IC package in the horizontal (x- and y-directions) is required before the package can be inserted vertically (in the z-direction) into well 310 and into contact with contact springs 315 and 320.
The left side of each of FIGS. 3A and 3C shows in phantom lines at 335 a packaged IC in a first position just prior to insertion in socket 300. The IC package is mis-aligned to the left by an amount 340 which would cause the end pin of the package to hit the end wall 345 of socket body 305 and thus to prevent further insertion into well 310. The right side of each of FIGS. 3A and 3C shows in phantom lines at 350 a packaged IC in a second position just as contact is being made between contact springs 320 of the socket and pins 355 of the IC package. In the second position, the IC package is mis-aligned to the right by an amount 360 which would cause the end 365 of the IC package to hit the end wall of socket body 305 and thus to prevent further insertion into well 310.
The left side of FIG. 3B shows in phantom lines at 370 a packaged IC in a third position just prior to insertion in socket 300. The IC package is mis-aligned to the left by a maximum amount 375 which would still permit insertion into well 310 of a socket without locator pins. The right side of FIG. 3B shows in phantom lines at 380 a packaged IC in a fourth position just prior to insertion in socket 300. The IC package is mis-aligned to the left by a maximum amount 385 which would still permit insertion into well 310 of a socket having locator pins.
Precise alignment of the IC package with the socket is difficult to achieve in a high-speed, automated, production environment. BIB's can be slightly misaligned in the burn-in board loader/unloader due to manufacturing tolerances and wear. Positioning of sockets on the BIB's can vary within some tolerance. The automated handler which positions the IC package over the socket can have some small positioning error from operation to operation due to manufacturing tolerances and wear. LIF sockets are in general less forgiving of mis-alignments than are ZIF sockets.
Beside the requirement to precisely align the IC package with the LIF socket, insertion of the IC package into well 310 requires a force which will cause pins of the IC package to deflect contact springs 315 and 320 outwardly. Removal of the IC package from the LIF socket also requires a force. The amount of force depends upon the particular design of the IC package and the socket, but is significant enough that it does not allow use of the package-handler tooling designed for dropping packaged IC's into and vacuuming packaged IC's out of ZIF sockets. To use LIF sockets in an automated setting such as on burn-in boards, tooling is required which will apply the needed insertion and removal forces, but without damage to the IC or the socket even when the two are mis-aligned. Bent IC pins, broken sockets and the like are not acceptable.
A new type of handler is needed to allow use of LIF sockets in such applications.